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Sinusoidal signals are essential in electrical engineering as we use them to
analyze and test circuit performance. All periodic signals can be represented
with sinusoidal signals of different amplitudes and phases using the Fourier
A typical sinusoidal signal is shown in Figure sinusoid. On the y-axis is the instantaneous
value of the sinusoidal voltage, and on the x-axis is time. Instantaneous values of
voltage change from -1V to 1V with time. We use the following parameters to
characterize sinusoidal signals: peak amplitude, peak-to-peak, average, RMS, period,
time-delay, and phase. We read peak amplitude, peak-to-peak, average, and RMS
values, on the y-axis in Figure sinusoid, whereas period, time delay, and phase on the
Figure 1: Vocabulary used in describing sinusoidal signals.
Parameters that are read on the y-axis.
We read the peak amplitude on the y-axis from the average value of the
signal (in this case, zero) to the signal’s maximum value (in this case, 1).
For signal shown in Figure sinusoid, the peak amplitude has a constant value of
The sinusoidal signal’s instantaneous value varies from -1 to 1V, and its value
depends on the x-axis.
Compared to the instantaneous value, the peak amplitude is always constant, and it
does not vary with time.
We measure peak-to-peak from the minimum value (in this case, -1) to the maximum
value (in this case, 1). For signal shown in Figure sinusoid, peak-to-peak voltage has a
constant value of .
RMS or root-mean-square is defined as . For signal shown in Figure sinusoid, and other
sinusoidal signals of this form, . Root mean square value is important because it
represents the equivalent amount of DC power.
Average value . For the signal shown in Figure sinusoid, the average value is because the
function has the same area under the function in the positive and negative
Parameters that are read on the x-axis.
We can represent sinusoidal signals as a function of time, Figure sin, or a function of
angle, Figure sinPh. Take a few minutes to see how the graphs are the same and how they
Figure 2: as a function of time.
Figure 3: Sinusoidal signal as a function of angle .
Period, T, is measured on the x-axis as the length of one full cycle of the sinusoidal
signal. For signal shown in Figure sinusoid, this value is .
Frequency, f, is defined as a reciprocal value of the period T, . It represents how fast
the signal is changing in time. In Figure sinF1F2, sinusoidal signals of two different
frequencies f are given.
Figure 4: Sinusoidal signals of different frequencies
Time delay and phase represent the lag (or lead) of one function with respect to
another in the time domain and frequency domain. For example, in Figure sinusoid, function
is time-delayed for with respect to . To find the time delay from the phase, we look
at how to represent the phase in terms of the product of frequency and time. Since
in the sinusoidal signal expression phase is added to term, the phase has the same
units as , and can be represented as the product of , , where represents the time
Figure 5: Sinusoidal signal as a function of angle with a phase shift of
Calculate the time-delay in nanoseconds that you would observe on an oscilloscope if
the frequency of the signal is f=0.159 GHz and the phase shift of the signal is .
Observe the three signals below, and change their amplitude and phase. Explain
qualitatively how are the signals changing when we move the sliders?